(a) Field of the Invention
The present invention relates to a compact zoom lens system comprising four lens groups.
(b) Description of the Prior Art
Known zoom lens systems comprising four lens groups are generally composed of a focusing lens group having positive refractive power, a variator having negative refractive power, a compensator having positive refractive power and a relay lens group having positive refractive power. As widely known, such a zoom lens system is arranged to be zoomed by moving the variator along the optical axis and to compensate for the movement of image surface, which is caused at that time, by moving the compensator along the optical axis. The lens system is focused by moving the focusing lens group.
Such known zoom lens systems comprising four lens groups have a disadvantage that the lens system becomes large in size due to the amount of movement of movable lens groups, i.e., the variator and compensator, is comparatively large. Especially when it is arranged to make the zoom ratio large, the above-mentioned amounts of movement become large. To make the zoom ratio large by making the abovementioned amounts of movement comparatively small, the power of the variator should be made large. When, however, power of the variator is made large, aberrations are aggravated; variation of aberrations caused when the variator is moved also become large, and it becomes considerably difficult to correct them. Moreover, to correct the above-mentioned aggravated aberrations and variation of aberrations, it is necessary to increase the number of lenses constituting the lens system, and, as a result, it becomes impossible to make the lens system compact.